This invention relates to fluid pressurizing devices for balloon catheters or the like, and more particularly relates to an improved device for actuating a screw plunger and monitoring the resulting fluid pressurization.
Fluid pressurization devices adapted for selectively applying and relieving a measured pressure on a closed volume of fluid have been developed for use in inflation and deflation of a balloon catheter used in angioplasty balloon procedures interiorly of blood vessels, or other types of balloon catheterization procedures. For example, U.S. Pat. No. 4,838,864 discloses a syringe device which inflates and deflates a catheterized balloon. The device uses a manually-operated screw plunger to achieve or maintain specific balloon pressure, and the pressure is monitored using an associated pressure gauge. Improved syringing and pressurization control is also described in U.S. Pat. Nos. 5,168,757; 5,713,242; and 6,796,959, all three of which are owned by the assignee of the present invention and are hereby incorporated herein in their entirety by reference. These patents disclose quick release mechanisms which enable rapid advancement of a plunger and alternatively allow threaded engagement with the screw plunger to achieve precise control during final pressurization of a balloon catheter.
A cross-sectional view of the device which is disclosed in U.S. Pat. No. 5,796,959 is shown generally in FIG. 1 herein (FIG. 1 herein corresponds to FIG. 4 of the '959 patent). As shown, the device 40 provides that a piston 48 is engaged with a plunger 68 inside a fluid displacement chamber 44 that is provided in a cylindrical syringe body or housing 42. A pressure gauge assembly 58 is threadably engaged with the housing 42, and the end 64 of the housing 42 is configured for engagement with a hose 54, such as a hose that is connected to a balloon catheter structure. The piston 48 has a sealing member 50 thereon which seals with an internal wall 72 of the housing 42. The plunger 68 can be retracted to pull fluid through the hose 54 into the device 40, and can be extended (or pushed in) to push fluid out of the device 40 and into the hose 54.
The plunger 68 can also be locked in place to prevent being pushed or pulled (i.e., to prevent macro movement of the plunger 68). Specifically, the device 40 includes a nut member 80 which can be moved into and out of engagement with a threaded portion 86 of the plunger 68. When the nut member 80 is not engaged with the threaded portion 86 of the plunger 68, as shown in FIG. 2, the plunger 68 can be extended or retracted (i.e., pushed or pulled) using macro movements. In contrast, when the nut member 80 is engaged with the threaded portion 86 of the plunger 68, as shown in FIG. 3, the plunger 68 is locked in place against macro movements, and can only be translated by using micro movements (i.e., by turning a knob 74 of the plunger 68).
To facilitate movement of the nut member 80, there are two link members 102, 104 which are engaged with the nut member 80 and which are retained on the device 40 by a pivot pin 106. The link members 102, 104 are positioned and configured to operate in tandem. As shown in FIGS. 2 and 3, the nut member 80 also includes a lever or grip portion 96 which can manipulated in order to shift the nut member 80, causing the nut member 80 to move into and out of engagement with the threaded portion 86 of the plunger 68. In order to move the nut member 80 into or out of engagement with the threaded portion 86 of the plunger 68, the link members 102, 104 must clear past ribs 120 (see FIGS. 2 and 3) which are provided on flanges 83 (see FIG. 1) which extend from the housing 42. Because the amount of force which is required to cause the link members 102, 104 to move past the ribs 120 depends on a plurality of part dimensions and tolerances, maintaining uniform detenting forces from one unit to the next, and from product line to product line, has proven challenging.
Another difficulty that can occur from time to time involves user convenience. Some users have found difficultly in reaching and engaging the lever 96 of the nut member 80 due to a combination of the manipulation required to perform the action and the operator's hand locations during certain procedures with the device 40, such as when the plunger 68 has been fully extended for vacuum and has to be locked into place. In such instances, the operator's hands can end up too far from the lever 96 to operate it without changing grip. During a disengage-withdraw plunger-reengage manipulation sequence (as occurs while drawing vacuum to pull down an interventional balloon after operation at pressure), users are forced to traverse the ribs 120 on the housing 42 twice by going one way and then back again the other direction in order to reengage the threaded plunger and hold it in a withdrawn position. Having to traverse the ribs 120 twice also occurs when manipulating to go from full vacuum or zero pressure to repressurization of the balloon.
Another disadvantage of the device 40 shown in the '959 patent relates to assembly. As shown in FIGS. 8-11 of the '959 patent, assembly requires alignment and sliding of the first link member 102 into the nut member 80, followed by upside down insertion of the second link member 104 into the nut member 80, and then 180 degree rotation of the second link 104 to align it with the first one 102. This requires manipulation and assembly time. Additionally, due to the need for free and independent rotation of the two link members 102, 104, it is not possible to be certain that these link members 102, 104 always stay in alignment with one another or are properly located in the nut member 80 to receive the pivot pin 106 during assembly.
Furthermore, precise longitudinal alignment is not generally possible with regard to the two link members 102, 104 and the nut member 80, and to both the pivot pin 106 and the threads 86 on the plunger 68. Specifically, each link member 102, 104 is free to pivot out of alignment slightly with the other and consequently allow the nut member 80 to slightly twist or deflect out of alignment with the plunger's axis during engagement and disengagement manipulations. Such twist is possible even though plunger 68 and pivot pin 106 are maintained in strict parallel alignment to one another. This undesirable deflection offers potential for a deleterious effect upon mating thread components resulting in uneven loading and occasional chipping of the most highly loaded threads during disengagement during maximum pressure use conditions.